Hypoglycaemia
Is the major hazard of insulin treatment,
and problems have increased in the drive to achieve “tight
control”. Patients may experience the symptoms of
hypoglycaemia when the blood concentration is less than
3·0 mmol/l.
However, individual susceptibility varies
considerably and it is interesting that some patients whose
control has been persistently very poor for long periods
appear to experience hypoglycaemic symptoms at levels a
little above this. The risks of hazard from hypoglycaemia are
small in most patients, but because they exist at all, patients
taking insulin are barred from certain occupations such as
driving trains or buses.
All patients taking insulin whose
diabetes is reasonably well controlled will experience
hypoglycaemia at some stage. At its mildest, it is no more
than a slight inconvenience, but at its severest, when
unconsciousness can occur, it is both a hazard and an
embarrassment.
Furthermore, manipulative patients can use
hypoglycaemia to threaten family and friends. This sword of
Damocles is ever present once insulin treatment has started,
and the need to use measures to avoid it requires constant,
indeed lifelong, vigilance. Hypoglycaemia occurs infrequently
in patients taking oral hypoglycaemics.
Symptoms
Most patients experience the early warning symptoms of
hypoglycaemia and can take sugar before more serious
symptoms develop. These warning symptoms are well known
and are described in the box.
Tremulousness and sweating
are by far the commonest symptoms, while circumoral
paraesthesiae is the most specific. Many patients have highly
individual symptoms of hypoglycaemia which range from quite
inexplicable sensations to peripheral paraesthesiae.
In three patients carpal tunnel compression resulted in tingling
fingers when they were hypoglycaemic, representing their sole
warning.
Neuroglyopenic symptoms and diminished cognitive
function follow if corrective action is not taken, with
progressive confusion and eventually unconsciousness and
occasionally convulsions. There is a prolonged debate as to
whether recurrent hypoglycaemia causes long-term intellectual
decline; the evidence in general is unconvincing although
major and recurrent episodes in childhood may have an
adverse effect in this regard.
Patients who become unconscious from hypoglycaemia
need urgent treatment.
Brain damage and death do not
normally occur because the blood glucose concentration
tends to increase spontaneously as the effect of the insulin
wears off and the normal counter-regulatory responses become
effective. Many diabetics, especially children, need reassurance
that they will not die in their sleep.
Nevertheless, a very small
number of otherwise unexplained deaths at night have been
reported in Type 1 diabetic patients (described as the “dead in
bed” syndrome) and no precise cause has ever been
established.
Deaths from prolonged hypoglycaemia are most
likely to occur after insulin overdoses, as a result either of a
suicide or murder attempt, but even in these circumstances
most patients recover
Causes of hypoglycaemia
In every patient taking insulin the blood glucose concentration
shows peaks and troughs, which can be most clearly shown by
home measurements of blood glucose. Since the lowest blood
glucose concentrations occur at different times in each patient,
it is a great advantage if individual patients know when their
own troughs are likely to occur.
The commonest times are
before lunch and during the night. Some patients in their
constant fear of developing diabetic complications drive their
blood glucose levels ever lower with disastrous consequences in
terms of hypoglycaemia.
Severe physical activity, such as swimming very long
distances, is a powerful stimulus of hypoglycaemia, and as much
as 40 to 50 g additional carbohydrate may be needed to prevent
it.
Hypoglycaemia in these situations is sometimes delayed for
several hours. Several well-known sportsmen and women with
diabetes show considerable ingenuity and perseverance in the
way in which they cope with their diabetes during international
competitions, by individual attention to food and insulin
intake, carefully timed blood glucose monitoring, and ready
availability of sugary fluids such as Lucozade at exactly the
right moment.
Hypoglycaemia is particularly likely to occur shortly after
stabilisation of new patients, as their insulin requirements may
decline considerably; their insulin dose should therefore always
be reduced before they leave hospital.
Hypoglycaemia is also troublesome when insulin
requirements insidiously decrease during the evolution of such
conditions as Addison’s disease, hypopituitarism, and
malabsorption syndromes.
Treatment and prevention of hypoglycaemia
Much of the skill required to manage insulin treated diabetic
patients is therefore devoted to achieving adequate control of
diabetes, yet avoiding hypoglycaemia. There are quite
straightforward measures which many patients neglect: they
must therefore at all times carry a supply of glucose both on
their person and in their cars, and take 10 to 20 g at the first
warning symptoms, preferably followed by a carbohydrate
snack.
The late RD Lawrence always demanded that his patients
should demonstrate that they were carrying their sugar supply
with them. This can take the form of sugar lumps, sweets
(non-diabetic), sugar gel or dextrose tablets.
They should take ample carbohydrate at times when blood
glucose troughs occur, notably mid-morning and bedtime,
and they must take appropriate amounts of additional
carbohydrate before and during vigorous exercise. Careful
blood glucose monitoring plays a crucial part in avoiding
hypoglycaemic episodes, and helps to restore warning of
hypoglycaemia.
Patients should try to avoid blood glucose
levels below 4·0 mmol/l. Appropriate insulin regimens that
need to be devised for individual patients are described in
chapters 5 and 6.
Glucagon
Glucagon is a hormone produced by the A-cells of the
pancreatic islets. It raises the blood glucose by mobilising the
glycogen stores in the liver (and therefore will not work after
prolonged starvation). It is given in a 1 mg dose by injection
most conveniently intramuscularly. It can also be used
subcutaneously or intravenously and is effective in five to
10 minutes.
It is of great value for bystanders of severely
hypoglycaemic patients who are unable to take oral glucose,
and can be injected by family members, nurses or doctors. It is
valuable in relieving stress in a home where a diabetic patient,
often a child, is prone to recurrent disabling attacks of
hypoglycaemia.
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